Capacitor discharge ignition system

ABSTRACT

In a capacitor discharge ignition system of the type known in the art in which energy from a battery is charged in a capacitor through a DC-DC converter and the charge thus stored in the capacitor is discharged through the primary winding of an ignition coil upon the conduction of a rectifier having a control electrode under the control of a gate control circuit thereby causing a high voltage in the secondary winding of the ignition coil, the improvement comprising the use of an arc duration extending ignition coil having a higher number of turns than the regular ignition coil and connected in series or parallel therewith, whereby a rapidly rising high voltage generated by the regular ignition coil is combined with a gradually rising, long duration, high voltage generated by the arc duration extending ignition coil to thereby produce a rapidly rising, long duration, high voltage at the output terminal of the ignition system.

United States Patent Kamiji CAPACITOR DISCHARGE IGNITION SYSTEM Primary Examiner-Laurence M. Goodridge Attorney, Agent, or FirmCushman, Darby & Cushman ABSTRACT In a capacitor discharge ignition system of the type known in the art in which energy from a battery is charged in a capacitor through a DC-DC converter and the charge thus stored in the capacitor is discharged through the primary winding of an ignition coil upon the conduction of a rectifier having a control electrode under the control of a gate control circuit thereby causing a high voltage in the secondary winding of the ignition coil, the improvement comprising the use of an arc duration extending ignition coil having a higher number of turns than the regular ignition coil and connected in series or parallel therewith, whereby a rapidly rising high voltage generated by the regular ignition coil is combined with a gradually rising, long duration, high voltage generated by the arc duration extending ignition coil to thereby produce a rapidly rising, long duration, high voltage at the output terminal of the ignition system.

1 Claim, 12 Drawing Figures [75] Inventor: Mamoru Kamiji, Kariya, Japan [73] Assignee: Nippondenso Co., Ltd., Kariya-shi,

Japan [22] Filed: Sept. 15, 1972 [2l] Appl. No.: 289,612

[30] Foreign Application Priority Data Sept. l7, 197] Japan 46-72578 Sept. 21, 1971 Japan.... 46-73632 July 3, l972 Japan 47-66825 [52] US. Cl. 123/148 E, 315/209 [51] Int. Cl. F02p 3/02 [58] Field of Search 123/148 E; 315/209 [56] References Cited UNITED STATES PATENTS 3,127,540 3/l964 Collins l23/l48 E 3,280,809 10/1966 lssler 123/148 E 3,489,129 l/l970 lssler et al. l23/l48 E 3,595,2l2 7/1971 Barnes l23/l48 E 3,635,202 l/l972 lssler et al. 123/148 E J2 00-00 CONVERTER GATE CONTROL f CIRCUIT mmgnssrzmu Fl G l I PRlOR oc-oc J2 CONVERTER 7 5 p l I l GATE 60 J b CONTROL 3/ CIRCUIT F l G 2 CONVERT ER 5 6b A L GAT e1 1 l Fab i f CONTROL -1:

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CONTROL I CIRCUIT 70 @"j b G SWITCHING b CIRCUIT 00-00 5 (j CONVERTER I g 8 CIRCUIT CAPACITOR DISCHARGE IGNITION SYSTEM The present invention relates to improvements in a capacitor discharge ignition system for an internal combustion engine of the kind used in automobiles and the like.

The capacitor discharge ignition system is generally employed for the purpose of ensuring a satisfactory ignition even when the spark has been fouled, that is, for

the purpose of improving the leak resistance property of the plug. In this system, therefore, the number of turns in the primary and secondary windings of the ignition coil are reduced to about one tenth of those in the ordinary ignition coils. This system is thus highly resistant to plug fouling, that is, it has a good leak resistance property. However, an essential drawback of this sys-' tem is that the duration of arc is short and thus a satisfactory ignition cannot be ensured under certain operating conditions of the engine. For this reason, efforts have been made to extend the duration of arc.

It is therefore an object of the present invention to provide an improved capacitor discharge ignition system capable of providing, as its output voltage, a high voltage which builds up rapidly and whose duration is long.

According to the present invention, there is provided an improved capacitor discharge ignition system of the tape adapted to store an energy from a battery in a capacitor through a DC-DC converter, and to discharge the charge stored in the capacitor through the primary winding of an ignition coil by the conduction of a rectifier with a control electrode under the control of a gate control circuit to thereby generate a high voltage in the secondary winding of the ignition coil, wherein the improvement comprises an arc duration extending ignition coil having a higher number of turns than the regular ignition coil and arranged to cooperate therewith, whereby the high voltages induced in the secondary windings of the ignition coils are combined to produce a resultant high voltage at the output terminal of the ignition system.

For a better understanding of the present invention reference is made to the following more detailed description taken in conjunction with the accompanying drawings, wherein:

FIG. I is an electrical wiring diagram of a conventional capacitor discharge ignition system;

FIG. 2 is an electrical wiring diagram of an embodiment of a capacitor discharge ignition system according to the present invention;

FIGS. 3 and 4 are wiring diagrams showing respectively and by way of typical example a known DC-DC converter and gate control circuit employed in the system illustrated in FIG. 2;

FIG. 5 is a diagram showing the output voltage waveforms of the system shown in FIG. 2;

FIG. 6 is an electrical wiring diagram of the capacitor discharge ignition system of FIG. 2 further including a switching circuit for protecting the breaker points;

FIG. 7 is an electrical wiring diagram showing an example of the switching circuit used in the system of FIG. 6;

FIG. 8 is an electrical wiring diagram of another embodiment of the capacitor discharge ignition system according to the present invention;

FIG. 9 is a diagram showing the output voltage waveforms of the system shown in FIG. 8;

FIG. 10 is an electrical wiring diagram of the capacitor discharge ignition system of FIG. 8 further including the switching circuit for protecting the breaker points;

FIG. 11 is an electrical wiring diagram showing a further embodiment of the capacitor discharge ignition system of the present invention; and

FIG. 12 is a diagram showing the output voltage waveforms of the system shown in FIG. 11.

FIG. 1 shows a known type of capacitor discharge ignition system in which a capacitor 5 is charged through a DC-DC converter 2 adapted to step up the voltage of a battery 1 and then the charge on the capacitor 5 is discharged through the anode and the cathode of a rectifier 4 with a control electrode (hereinafter referred to as SCR) conduced by the output signal of a gate control circuit 3 and a primary winding 6a of an ignition coil 6, thereby generating a rapidly rising, high voltage in an ignition secondary coil 6b. As previously mentioned, the numbers of the turns in the primary winding 6a and secondary winding 6b of the ignition coil 6 are reduced to about one tenth of those of the ordinary ignition coils.

Referring now to FIG. 2 illustrating an embodiment of the present invention, numeral 1 designates a battery constituting the power supply, numeral 2 designates a DC-DC converter for stepping up the voltage of the battery 1 and consisting of a conventional DC-DC converter as shown in FIG. 3. Numeral 3 designates a gate control circuit for a rectifier 4 with a control electrode, the circuit being adapted to receive circuit interruption signals from breaker points 8 mounted in the ignition distributor (not shown) to thereby conduct the SCR 4 and consisting of a conventional circuit as shown in FIG. 4. Numeral 5 designates a storage capacitor, 6 an ignition coil of the same construction as used in conventional capacitor discharge ignition systems. As previously mentioned, the number of turns in both the primary winding 6a and secondary winding 6b of this ignition coil is reduced to about one tenth of those of the ignition coils in conventional ignition systems. Numeral 7 designates an arc duration extending ignition coil provided in addition to the ignition coil 6, with the number of turns in both of its primary winding 7a and secondary winding 7b being greater than those of the ignition coil 6 (the numbers of the turns are about the same with those of ignition coils in conventional ignition systems) and adapted such that when the primary current supplied to the primary winding 7a is interrupted by the breaker points 8 constituting switching means, a high voltage is induced in the secondary winding 7b. Numeral 9 designates a high voltage proof diode and numeral 10 designates an arc extinction capacitor. The secondary winding 7b of the ignition coil 7 is connected in parallel with the secondary winding 6b of the ignition coil 6 through the diode 9.

With the construction described above, the operation of this embodiment will now be explained. When the breaker points 8 constituting the switching means open so that the primary current supplied to the primary winding 7a of the arc duration extending ignition coil 7 is interrupted, a gradually rising, high voltage of a long duration is generated in the secondary winding 7b due to the higher number of turns and hence the increased self-inductance of the ignition coil 7. In-this case, if the capacitor 5 has been charged previously through the DC-DC converter 2, the SCR 4 is conducted through the gate control circuit 3 by an opening or an interruption signal from the breaker points 8, thereby discharging the charge on the capacitor through the anode and the cathode of the SCR 4 and the primary winding 6a of the ignition coil 6. Since the numbers of the turns in the primary and secondary windings 6a and 6b are small as compared with those in the ordinary ignition coils and their self-inductances are also small, a rapidly rising, high voltage is generated in the secondary winding 6b of the ignition coil 6 as in the conventional capacitor discharge ignition systems. The experiments conducted by the inventor showed that the waveforms shown by solid lines a and b in FIG. 5(A) were produced when the voltages generated in the secondary windings 6a and 7a of the ignition coils 6 and 7 were measured with the ignition coils separated electrically from each other. In the arc duration extending ignition coil 7, its primary current is very small as compared with the primary current in the conventional capacitor discharge system ignition coil 6 and thus its secondary current is also small. Therefore, if its circuit design is such that the secondary winding receives the same amount of energy as in the conventional capacitor discharge system ignition coil, then the duration of the secondary current (arc duration) tends to be long relative to that of the ignition coil employed in the conventional capacitor discharge systems. Further, if the secondary windings 6b and 7b of the ignition coils 6 and 7 are connected in series and a composite voltage generated at an output terminal P is measured, then it shows that the value ofthe voltage generated in the secondary windings 6b and 7b, respectively, decreases under the influence of the impedance of another secondary winding. This has also been found by experiments conducted by the inventor. In the system of the present invention, however, the secondary windings 6b and 7b are connected in parallel and moreover the diode 9 is provided to prevent the voltage induced in the secondary winding 7b from being applied to the secondary winding 6b. Therefore, the secondary windings 6b and 7b are substantially separated electrically from each other, thereby preventing any drop in the generated voltage due to the consumption of energy by another secondary winding. The reason is that the flow of current to the secondary winding 7b caused by the voltage generated in the secondary winding 6b is practically prevented because of the higher number of turns and hence the increased impedance of the secondary winding 7b, while the current flow to the secondary winding 6b caused by the voltage generated in the secondary winding 7b is blocked by the diode 9. Consequently, the voltage generated in the secondary windings 6b and 7b, respectively, is not influenced by another secondary winding. In this manner, the composite voltage generated at the output terminal P does not decrease as compared with the generated voltage measured with the ignition coils 6 and 7 separated electrically from each other, and this is evident from the waveform indicated by a broken line c in FIG. 5(A) obtained from the same experiments by the inventor. In FIG. 5(A). a solid line d indicates the waveform of the voltage generated in the ignition coil 6, which was obtained when the diode 9 was provided and the ignition coil 6 was electrically separated from the ignition coil 7. As will be seen from a comparison between the voltage waveforms a and c, it is now evident that the provision of the arc duration extending ignition coil 7 in addition to the conventional capacitor discharge system ignition coil 6 produces a voltage waveform at the output terminal P whose duration is considerably long as compared with that obtainable when the conventional capacitor discharge system ignition coil is employed alone. In other words, a high-tension output voltage is obtained which has a very rapid rate of increase and a longer duration. Here, it is to be noted that when an arc occurs at the spark plug, the voltage at the output terminal P is delayed under the influence of the impedances of the secondary windings 6b and 7b and therefore the actual arc duration t (not shown) tends, as shown in FIG. 5(B), to be longer than a time t' in FIG. 5(A) which is necessary for the voltage to decrease to the minimum value required for the arc.

FIG. 6 illustrates another embodiment of the present invention which is essentially the same as that of FIG. 5, except that this embodiment further includes a switching circuit 11 for protecting the breaker points 8. The switching circuit 11 may comprise a conventional circuit such as is shown in FIG. 7 and it is connected between the primary winding 7a of the arc duration extending ignition coil 7 and the ground to break and make theprimary current to the arc duration extending ignition coil 7 in response to the opening and closing of the contact points 8. The control terminal a of the switching circuit 11 is connected to the DC-DC converter 2 and another control terminal h is connected to the breaker points 8 and the control terminal of the gate control circuit 3. The primary current in the arc duration extending ignition coil 7 is controlled through the switching circuit 11 according to the opening and closing of the breaker points 8 and at the same time control signals can be sent to the gate control circuit 3. A large portion of the primary current in the arc duration extending ignition coil 7 flows through the switching circuit 11 and therefore a very small portion of the current flows to the contact points 8. When this switching circuit 11 is employed, the output voltage of a magneto synchronized with the rotation of the engine may be utilized as a source of ignition signals in place of the breaker points 8, thereby providing a contactless ignition system.

FIG. 8 illustrates a further embodiment of the capacitor discharge ignition system of the present invention and this embodiment differs from that of FIG. 2 in that the secondary winding 7b of the arcduration extending ignition coil 7 is connected in series with the secondary winding 6b of the ignition coil 6. With this construction, the embodiment of FIG. 8 operates as follows. When the breaker points 8 open, the primary current supplied to the primary winding 7a of the arc duration extending ignition coil 7 is interrupted and, as the ignition coil 7 has a higher number of turns and hence a large self-inductance. a high voltage with a gradual rise and of a long duration is produced in the secondary winding 7b. At this time, if the capacitor 5 has been charged previously through the DC-DC converter 2, the SCR 4 is conducted through the gate control circuit 3 by an opening or a circuit interruption signal generated by the breaker points 8. When this occurs, the charge on the capacitor 5 is discharged through the anode and the cathode of the SCR 4 and through the primary winding 6a of the ignition coil 6. In this case, since the number of turns in the primary winding 6a is small compared to those in the ordinary ignition coils and thus its self-induction is also small, a high voltage is produced in the secondary winding 6b of the ignition coil 6, which builds up as rapidly as in the case of conventional capacitor discharge ignition systems. Consequently, the high voltages generated in the secondary windings 6b and 7b are superposed, producing at the output terminal P an output voltage which builds up rapidly and is of a long duration. The waveform of this output voltage is indicated by a solid line c in FIG. 9(A) in which a broken line b indicates the voltage generated in the secondary winding 6b of the ignition coil 6 and a broken line a indicates the voltage generated in the secondary winding 7b of the arc duration extending ignition coil 7. If the spark plug is connected to the output terminal P, then the voltage waveform shown in FIG. 9(B) is produced thereat and the arc duration of the plug becomes long as shown by a time in the figure. The output voltage waveform of the conventional capacitor discharge ignition system shown in FIG. 1 is indicated in FIG. 9(C) and its arc duration time t, is indicated in FIG. 9(D).

FIG. 10 is a still further embodiment of the present invention and this embodiment is essentially the same as that of FIG. 8, except that the switching circuit 11 is additionally provided to protect the breaking points 8. The switching circuit 11 operates in the same manner as described in connection with FIG. 6.

FIG. 11 illustrates a still further embodiment of the present invention. In this embodiment, a series circuit of the charge and discharge capacitor 5 and the primary winding 6a of the ignition coil 6 is connected in parallel with a series circuit of another charge and discharge capacitor 12 and the primary winding 7a of the arc duration extending ignition coil 7, and the secondary winding 7b of the arc duration extending ignition coil 7 is connected in series with the secondary winding 6b of the ignition coil 6. Consequently, a high voltage generated in the secondary winding 6b of the ignition coil 6 with the same rapid rate of increase as in conventional capacitor discharge systems and a gradually rising, short duration, high tension voltage generated in the secondary winding 7b of the ignition coil 7 are superposed with the result that a rapidly rising, long duration, output voltage is produced at the output terminal P. The waveform of this output voltage is indicated by a solid line c in FIG. 12(A) in which a broken line a indicates the voltage generated in the secondary winding 6b of the ignition coil 6 and a broken line b indicates the voltage generated in the secondary winding 7b of the arc duration extending ignition coil 7. If the spark plug is connected to the output terminal P, then the voltage waveform shown in FIG. 12(B) is obtained and the arc duration of the plug becomes long as shown by a time in the figure. The output voltage waveform of the conventional capacitor discharge ignition system shown in FIG. 1 is indicated in FIG. 12(C) and its arc discharge duration t, is indicated in FIG. 12(D).

While, in the embodiments of the invention so far described, the separately manufactured ignition coils 6 and 7 have been employed, the ignition coils 6 and 7 may comprise two ignition coils each composed of a primary and a secondary winding wound around a soft iron core with the cores being placed in a single case and magnetically separated from each other.

What we claim is:

l. A capacitor discharge circuit for generating from a battery source high voltage pulses for application to a spark plug in response to operation of contact points comprising a DC-DC converter coupled between a first terminal of the battery source and a first connection point, a control rectifier connected between said first connection point and a second terminal of the battery source, said control rectifier additionally having a control electrode, a gate control circuit coupled between the first battery terminal and the control electrode of said control rectifier and operated by the Contact points to apply control signals to said control electrode, a first series circuit comprising a first capacitor and the primary winding of a first ignition coil connected between the first connection point and the second battery terminal, a second series circuit comprising a second capacitor and the primary winding of a second ignition coil connected in parallel with said first series circuit, the secondary windings of said first and second ignition coils being connected in series with each other between the second battery terminal and the spark plug, and wherein the primary and secondary windings of said second ignition coil have substantially greater number of turns than the primary and secondary windings of said first ignition coil. 

1. A capacitor discharge circuit for generating from a battery source high voltage pulses for application to a spark plug in response to operation of contact points comprising a DC-DC converter coupled between a first terminal of the battery source and a first connection point, a control rectifier connected between said first connection point and a second terminal of the battery source, said control rectifier additionally having a control electrode, a gate control circuit coupled between the first battery terminal and the control electrode of said control rectifier and operated by the contact points to apply control signals to said control electrode, a first series circuit comprising a first capacitor and the primary winding of a first ignition coil connected between the first connection point and the second battery terminal, a second series circuit comprising a second capacitor and the primary winding of a second ignition coil connected in parallel with said first series circuit, the secondary windings of said first and second ignition coils being connected in series with each other between the second battery terminal and the spark plug, and wherein the primary and secondary windings of said second ignition coil have substantially greater number of turns than the primary and secondary windings of said first ignition coil. 